In recent years, a flat panel display has been widely used. A representative example of the flat panel display is a liquid crystal display.
Generally, the liquid crystal display (LCD) requires a backlight unit that provides uniform light throughout a screen, unlike a conventional CRT.
Specifically, the backlight unit is configured to provide uniform light from a rear surface of the liquid crystal display, in which a light source LED is disposed on one side of a light guide plate, and the light guide plate is provided with a reflector on a lower surface thereof so as to transmit a light emitted from the light source upwardly.
In this state, the light generated by the light source is transmitted upwardly by the light guide plate and the reflector, and the light transmitted to the upper portion is uniformly moved upwardly through a light-condensing sheet.
At the same time, a separate reflective polarizing sheet is provided on the upper portion of the light-condensing sheet to transmit only the light of a specific polarization upwardly, thereby transmitting the light that has been stably condensed to the outside.
As the light-condensing sheet, a sheet having a general prism may be applied.
In addition, when a separate reflective polarizing sheet is provided on the upper portion of the light-condensing sheet, the brightness of the liquid crystal display can be increased.
As described above, in the backlight unit, a light generated from the light source provided on the side is transmitted upwardly by the light guide plate and the reflector, and the light transmitted upwardly is uniformly condensed through the light-condensing sheet.
On the other hand, in the case where a reflective polarizing sheet is provided in the backlight unit, since the brightness of the liquid crystal display can be raised, it is widely used. However, when the light-condensing sheet having a plurality of prisms is bonded to the reflective polarizing sheet, an upper end portion of the prism having an inclined plane forms a bonding surface and is eliminated.
Thus, the upper end portion of the prism is eliminated, and the bonding surface is formed with the reflective polarizing sheet to be bonded, so that the reflective polarizing sheet and the light-condensing sheet can stably maintain the bonding state.
However, since the upper end portion of the light-condensing sheet is eliminated due to the bonding with the reflective polarizing sheet as described above, the inclined plane is eliminated at a portion where the bonding surface is formed, so that the efficiency of the light-condensing sheet for condensing the light transmitted from below is reduced.
Particularly, when light is transmitted through the bonding surface where the reflective polarizing sheet and the prism are bonded, a bonding surface line is visually observed, or a color shift occurs due to the optical interference phenomenon of the reflective polarizing sheet composed of a multilayer thin film. Accordingly, there is a problem that a screen quality is deteriorated.
In addition, an unintentional moire phenomenon due to optical interference with a liquid crystal panel may be caused by the bonding surface line having a specific pattern.